1. Field of the Invention
The present invention relates to a method for measuring an edge profile of a semiconductor wafer and a device for measuring the profile used therefor, specifically to a method for measuring the profile and to a device for measuring the profile used therefor that prevent scratches and flaws from being generated on semiconductor wafers due to contact between semiconductor wafers and measuring instruments, as being applicable to large-diameter wafers.
2. Description of the Related Art
When surfaces of semiconductor wafers are machined in a slicing process or a polishing process, peripheries of wafers likely contain acute-angled edges, causing cracking or chip on wafers when they come into contact with transferring devices. For this reason, wafers are subjected to edge-preparation to remove acute-angled edges on peripheries of wafers to form peripheries in a rounded or chamfered profile. Edge profiles and edge dimensions of wafers formed by chamfering need to be determined and finished within ranges specified by standards established by industrial organizations or customer requirements. Thus, in wafer manufacturing process, acceptance inspection is conducted to measure edge profiles of wafers to confirm whether they are within predetermined ranges after, for example, chamfering or finishing polishing.
In relation to measuring edge profiles of wafers, for example, Japanese Patent Application Publication No. 07-208969 describes a method where a wafer is rotatably supported while allowing the wafer to rotate around a point on the periphery end surface thereof as the center of rotation, and the wafer is rotated around the point on the periphery thereof as the center while a stylus of a profile measuring instrument is pressed against the periphery end surface of the wafer to measure contact positions of the stylus relative to rotation angles. Then, an edge profile of the wafer is elucidated by calculating a contour profile of the wafer using coordinate transformation by means of a calculation means.
The method described in Japanese Patent Application No. 07-208969 may cause scratches on wafers due to measurements with a stylus pressed against wafers, while generating dust due to physical contact to deposit on the wafer, likely causing wafer defects.
In order to prevent scratches and defects from being generated due to measurements of edge profiles of wafers, used is a method that measures an edge profile by measuring a projected shadow by emitting parallel light to a peripheral edge region of a wafer.
FIG. 1 shows a conventional method for measuring an edge profile of a wafer using a projection method. The measuring device shown in the figure comprises an emitting part 16 to emit parallel light to an edge region of a wafer, and a projection part 17 where a shadow of the edge region of the wafer is projected by the parallel light. An edge profile of a wafer 12 is measured using the measuring device shown in the figure by disposing the wafer between the emitting part 16 and the projection part 17, then radiating parallel light to the wafer by the emitting part 16, projecting a shadow on the projection part 17, and applying image processing to the shadow to calculate dimensions of the chamfered region.
The method for measuring an edge profile of a wafer using the projection method enables profile measurement to be performed without, for example, a stylus in contact with edge regions of wafers, thus preventing scratches on edge regions and flaws on surfaces of wafers from being generated due to measurement.
When the wafer becomes large in diameter, however, loads exerted to the supporting points for supporting the wafer will increase as well as the self-weight of wafer, thus increasing strain exerted to the wafer, resulting in irregular flexure at the edge region. Thus, when parallel light is emitted to the wafer to project its shadow on the projection part, the contour of the shadow will be blurred. In addition, the emitted parallel light would project shadows covering a wide range of the chamfered region of the wafer in the direction along the chamfered surface and if the profile is irregular in the direction of the parallel light, the contour of the projected shadow will also be blurred. Due to these factors, dimensions of chamfered regions cannot be calculated accurately by image processing. Thus, the method for measuring a profile using the projection method has not been applicable to measurement of large-diameter wafers, especially wafers of more than 400 mm in diameter.
In addition, wafers may be provided with notches on their peripheries as indicators of crystal orientation. The method for measuring a profile using the projection method cannot project shadows of notches, thus unable to measure profiles thereof. In some cases, orientation flats may be provided on peripheries of wafers as indicators of crystal orientation by forming straight portions in parts of the peripheries of wafers. Although the periphery of wafer at the orientation flat is straight, the chamfered profile such as the radii of round corners on the straight portion gradually changes due to its processing method. Because of this, the projection method does not provide shadows thereof, thus unable to measure the profiles thereof.